1. Field of the Invention.
The present invention relates to an oxide film forming method, a gas drier, a rotating coater, a vacuum treatment apparatus, a heat treatment apparatus, a charged particle flow irradiating apparatus, a plasma treatment apparatus, an electrostatic absorber, an interatomic force microscope, an X-ray irradiating apparatus, and a clearing equipment.
2. Description of the Related Art.
(Oxide Film Forming Method)
Reference is made to the prior art in this field, in particular, to the use of silicon substrates as the substrate body.
As one of the methods of forming an oxide film on a surface of a silicon substrate, the so-called thermally oxidizing method has been known.
In this method, after a natural oxide film is removed by contacting fluoric acid solution to a silicon substrate, the silicon substrate is cleaned with ultra pure water and dried, and then dry oxygen or dry oxygen mixed with an inert gas is contacted to the silicon substrate to form an oxide film.
In this method, which involves a process to heat a silicon substrate from a room temperature to a specified temperature required for oxidization, for instance, from 800° C. to 1000° C., an oxide film having a thickness, for instance, from 1.5 to 3.5 nm is formed. The oxide film formed in the heating process, however, is not fine. For this reason, as a percentage of a thickness of oxide film (formed until the silicon substrate is heated up to a specified temperature) against the total thickness of an oxide film (finally formed through all processing steps) is high, an oxide film having an excellent insulating capability is not formed, which is a deficiency needing to be overcome. A discussion is made hereinafter of the importance of an oxide film having a high insulating capability with reference to a case of forming a MOSLSI oxide film.
Progress in the field of LSI technology is very fast, and a DRAM having a storage capacity of 4M bit or more has been put into practical use. In order to manufacture such a high performance electronic device, namely a device having an ultra high degree of integrity, it is desirable to employ a high performance manufacturing process having a high degree of process controllability that is little affected by uncertain factors. One such example of a high performance manufacturing process is the ultra clean process.
For instance, cleaning the process atmosphere is required to form an oxide film having a high insulating capability for forming an oxide film only at a specified temperature, while suppressing formation of an oxide film while the silicon substrate is being heated for the purpose to form an oxide film having a high insulating capability. An inert gas or a bulk gas atmosphere without moisture or oxygen is required.
Also, cleaning the process atmosphere is required to reduce impurities taken into an oxide film when the oxide film is being formed. When a clean process atmosphere is used, a lap density in the oxide film and on an interface between the oxide film and the silicon is reduced, as well as realizing an electrically stable semiconductor device.
As described above, cleaning the process atmosphere is indispensable for realization of an ultra fine LSI.
It is an object of the present invention to provide an oxide film forming method enabling formation of an oxide film having a high insulating capability on a surface of a substrate body.
(Gas Drier)
Conventionally, the first to third technologies as described below are driers known to have been used to dry this type of object.
The first technology provides a spin drier, which dries an object needing to be dried by rotating the object at a high rotating speed for blowing away liquid adhered to a surface of the object. With this technology, it is possible to dry an object by also blowing away liquid deposited in very fine concave sections or a surface of the object, and it is also possible to prevent a natural oxide film from growing on a surface of the object (for instance, a silicon wafer) during the drying process by purging the inside of the device with nitrogen. Also, it is possible to prevent generation of static electricity due to a high speed rotation of an object being dried as well as to prevent minute particles from depositing on the object due to static electricity. Such prevention can be achieved by installing inside the device an ionizer with the electrode section coated with a ceramic material.
The second technology relates to an IPA vapor drier, which dries an object needing to be dried by heating IPA (Isopropyl Alcohol) inside the device to generate IPA vapor and replacing liquid (for instance, ultra pure water) deposited on a surface of the object being dried with the IPA which has a high volatility. As the IPA vapor can easily go into very fine concave sections on a surface of the object, it is possible to completely dry even the inside of very fine concave sections on a surface of the object. Also, the IPA has a function to remove static electricity. It not only removes static electricity on a surface of the object, but also suppresses generation of static electricity. As such, it is possible to suppress deposition due to static electricity of minute particles onto a surface of the object being dried.
The third technology relates to a non-reactive gas drier, which dries an object by blowing a gas not reacting with the object, onto a surface of the object to blow off liquid (for instance, ultra pure water) deposited on the surface. By reducing a quantity of moisture contained in a gas to an extremely small quantity (for instance, 1 ppb or below), it is possible to effectively remove residual absorptive molecules (for instance, water molecules) remaining on a surface of the object being dried. Also, by sealing the device against the external air and supplying an inert atmosphere gas into the device, it is possible to prevent a natural oxide film from being generated on a surface of the object (for instance, a silicon wafer) during such a process.
However, each of the conventional technologies described above has the following problems, respectively.
In the first technology, after liquid (for instance, ultra pure water) is blown off from a surface of an object to be dried, molecules of the liquid still remains on the surface of the object to be dried or have been absorbed into the object itself.
In the second technology described above, after liquid (for instance, ultra-pure water) deposited on a surface of an object to be dried has been replaced with the IPA vapor, IPA molecules and liquid molecules (for instance, molecules of water) remain on the surface of the object to be dried.
In the third technology above, static electricity is generated on a surface of an object to be dried due to friction between a surface of the object to be dried and a dry gas, and fine particles are easily deposited on that object surface.
It is an object of the present invention to provide a drier which can dry an object without leaving any remaining liquid, without causing a charge in quality such as growth of a natural oxide film on a surface of the object, and also without allowing generation of static electricity and deposition of fine particles on a surface of the object.
(Rotating Coater)
Conventionally, for instance, in a process to manufacture semiconductors, a technology to homogeneously spread various types of materials on a wafer surface by spreading a liquid material on a Si wafer and then removing the solvent by means of heating has been used in a wide range of applications. For instance, the photo resist used in a lithography process is the representative one. Also, such thin films as a SiO2 film, PSG film, and AsSG film are formed by spreading each material dissolved in an inorganic or an organic solvent through rotation on a wafer and depositing the material on a surface of the wafer. In this process, a thin film such as a SiO2 film can be formed at a low temperature, and this thin film has been used as an interlayer insulating film for multi-layered wiring or as an etching mask in a multi-layered photo resist process.
Next detailed are problems in the prior art, taking up a resist spreading process as an example, with reference to FIG. 3-3, and FIG. 3-4. FIG. 3 is a block diagram of a conventional type of rotating coater. The conventional type of resist spreader comprises a wafer holder 302 based on, for instance, a vacuum absorbing system to hold a sample 301 such as, for instance, a Si wafer, a nozzle 303 (a means for supplying a liquid material or a material behaving as a liquid to be spread) having a function to drip resist, and a vessel 304 with the above components provided therein. Herein, the wafer holder 302 has also a rotational function.
FIG. 3-4 shows a process to spread resist. Resist is dripped onto a surface of a wafer from a nozzle (a means for supplying a liquid or liquid like material to be spread) 403 (step a). The wafer holder 402 rotates, and resist 404 is spread due to the centrifugal force (step b). Furthermore, solvent in the resist is evaporated, and a homogeneous resist film is formed (step c). Then, a film thickness of the resist is decided according to such factors as r.p.m. of the wafer holder 402 and/or viscosity of the resist. If a resist having a viscosity of, for instance, 25 cp is dripped on a Si wafer and the Si wafer is rotated at the rotating speed of 4000 rpm for 40 sec, a film thickness of the resist becomes 1.25 μm. Also, in the conventional type of technology for spreading resist through rotation, the resist temperature, environmental temperature as well as environmental humidity inside the device is controlled to achieve homogeneity in the resist film thickness.
Generally, humidity in the device is from 40 to 50% like that in a clean room.
In the conventional type of device, however, particles are deposited on a wafer, in and on resist. Also, if resist is spread through rotation on an insulating material such as an oxide film, sometimes unevenness in spreading occurs, and the resist is not spread in some sections. This phenomenon occurs in spreading not only resist, but also SiO2, PSG, and AsSG to form a thin film. So the present inventor investigates why the unevenness in spreading occurs on such a thin film as a resist film. As a result, the inventor obtained several reasons to guess that the unevenness in spreading may occur because a wafer is locally electrified due to friction between the wafer rotating at a high rotating speed of several thousand rpm and the resist and/or a gas inside a vessel and a repelling force is resultingly generated between the electrified portion of the wafer and the resist.
Real reasons for unevenness in spreading have not been found yet, and for this reason any countermeasures to prevent electrification in spreading resist through rotation to form, for instance, a resist film have not been taken at all.
The present invention was made in the light of the circumstances as described above, and it is an object of the present invention to provide a rotating spreader which can form a spread film with any particle deposited thereon and without generating unevenness in spreading on a surface of a sample.
(Vacuum Treatment Apparatus)
FIG. 4-4 shows configuration of a general vacuum carrier/treatment apparatus.
In FIG. 4-4, designated at the reference numeral 401 is a load/lock chamber, at 402 a carrier chamber, and at 403 a reaction chamber. These three chambers 401-403 are connected to each other in a form of chain. In an actual process, at first a wafer is put in a holder such as a cassette, then a door 404 is opened for setting under the atmospheric pressure, and then the door is closed. Then, air in the load/lock chamber 401 is discharged by a vacuum pump 405 to realize a vacuum of around 10−6 Torr therein. Then, also air in the carrier chamber 402 is discharged by a vacuum pump 408 to realize vacuum of around 10−8 Torr therein. A gate valve 407 provided between the load/lock chamber 401 and the carrier chamber 402 is then opened, the wafer is carried therethrough, and then the gate valve 407 is closed. Then, air in the reaction chamber 403 is discharged by a vacuum pump 408 to realize vacuum of around 10−10 Torr therein, a gate valve 409 provided between the carrier room 402 and the reaction chamber 403 is opened, and a wafer is carried therethrough. With the operations described above, the load/lock chamber 401 and the reaction chamber 403 in which the vacuum degree has been dropped relative to the atmospheric pressure are not directly exposed to the same atmosphere during transfer of a wafer, and a high vacuum degree can always be maintained in the reaction chamber 403. When a wafer is carried up to the reaction chamber 403, the gate valve 407 is closed, the reaction chamber 403 is sealed, and air in the reaction chamber is furthermore discharged by a vacuum chamber. In the state as described above, a specified gas is introduced into the reaction chamber 403 through, for instance, a gas pipe 410, to carry out processing.
When the process if finished, again the gate valve 409 is opened, and the wafer is carried to the carrier chamber 402. Then, after the gate valve 409 is closed to shut off the reaction chamber 403, the gate valve 407 is opener and the wafer is carried to the load/lock chamber 401.
After the wafer is carried to the load/lock chamber, the gate valve 407 is closed to shut off the carrier chamber 402 from the load/lock chamber 401. Then, a gas is introduced through a gas inlet port 411, air in the load/lock chamber 401 is leaked in to decrease the vacuum degree therein relative to the atmospheric pressure, and the wafer is taken out under the atmospheric pressure. Thus, when taking out a wafer from the load/lock chamber, a gas such as dry nitrogen gas or argon gas is introduced via leaking into the chamber.
In the conventional technology as described above, however, there is a big problem relating to leakage in the load/lock chamber. Namely, when, for instance, a dry nitrogen gas is introduced from a gas inlet port, particles rise up in the load/lock chamber and fall onto a wafer; and/or a wafer is electrified due to such causes as static electricity generated because of the nitrogen gas flow, and a large quantity of particles deposit on the wafer. For these reasons, in the conventional type of load/lock chamber, a wafer can be contaminated by deposited particles, and the yield caused to go down. It should be noted that, although various countermeasures such as decreasing a flow rate of nitrogen gas used for leaking in a chamber have been proposed to solve, for instance, such problems as electrification, electrification of a wafer is too effective for causing deposition of particles thereon. As such, the countermeasures have not been shown to be adequately effective.
(Heat Treatment Apparatus)
Conventionally, for instance, in a thermally oxidizing furnace, a gas mixture of oxygen, inert gas, or other gases is introduced into a furnace tube comprising a quartz tube heated by means of electric resistance heating method, and the gas mixture is brought into contact with a heated silicon substrate.
In this case, in order to form an oxide film having a high reliability, a furnace tube itself, in which an oxidizing reaction process is executed, must not be contaminated by particles, and the tube is required to be cleaned as much as possible.
Also, in order to manufacture electrically stable semiconductor devices by reducing defects of an interface between an oxide film and a silicon substrate, it is necessary to reduce a number of particles deposited on the silicon substrate as much as possible.
Thus, ultra cleaning in the atmosphere for a heat treatment process is indispensable for realization of ultra fine LSI.
In the conventional type of apparatus, however, gas introduced therein flows, contacting a quartz tube, which is an insulating body, and a quartz susceptor holding a silicon substrate. The quartz tube and the quartz susceptor are electrified, and a number of particles are deposited thereon. Such particles can potentially contaminate the silicon substrate. Also, when a silicon substrate is carried into or out from the furnace tube, or during a reaction, the silicon substrate itself contacts the gas, so that particles may easily deposit on the silicon substrate.
The present invention was made in the light of the circumstance described above, and it is an object of the present invention to provide heat treatment apparatus which can form an oxide film having a high reliability and execute such processings as an oxidizing reaction.
(Charged-particle Flow Irradiating Apparatus)
The technology of irradiating charged particles such as electrons or ions onto a surface of a sample has been widely used for such purposes as analysis of the sample or production of semiconductors. For instance, as a device for irradiating electrons, a scanning electron microscope (SEM) or an electron beam direct drawing apparatus (EB) has been known.
The former is an analyzer used to observe a state of a sample's surface in detail, while the latter is a device for forming fine patterns with resist.
Description is made for a SEM based on the conventional configuration with reference to FIG. 6-4. In this figure, the reference numeral 401 indicates an electron gun, and electrons generated therein form an electron beam 402, which is a flow of charged particles. These electrons are accelerated to about 50 KeV, being irradiated onto a sample.
When the electron beam 402 is irradiated onto a surface of a sample, secondary electrons 402 are released from a surface of the sample 404. The secondary electrons are detected by a detector 407. As the efficiency of releasing the secondary electrons changes according to irregularity of the surface of the sample 404, so it is possible to observe a state of the sample's surface.
Next a description is made for an ion implanter having a conventional configuration.
FIG. 6-5 is a cross sectional view of a MOS transistor, illustrating a state where a source 502 and a drain 503 for MOSFET is formed by implanting As ions 501 by means of ion implantation.
The ion beam is also applied to a gate electrode 504, but the gate electrode 504 is separated with a gate insulating material 505 from a silicon substrate 506, so that an electric charge can not escape therefrom.
In a SEM having the configuration as described above, electrons each having a negative charge are irradiated onto a surface of a sample, so the sample is electrified. This electrification disadvantageously gives effects over the incoming electrons or the secondary electrons.
As a result, various problems occur, and a resolution of an insulating body can not be raised in a SEM, and also high pattern precision can not be obtained in an electronic beam exposing apparatus. For instance, if the sample 403 is a Si wafer, and the surface 404 is a SiO2 film having a thickness of 1000 Å, negative electric charge 408 is accumulated on a surface of the SiO2 film when the electron beam 402 is applied to the surface. As the SiO2 film is an insulating film, the negative electric charge generates a new electric line of force on the sample's surface 404. Various effects, including a curved orbit trail of the incoming electrons 402 or secondary electrons 405, occur due to the influence by this electric line of force (electric field). When electrification as described above occurs, a precision of observable images remarkably drops. Concretely, a phenomenon that an object pattern looks blurred and white occurs on a screen.
Conventionally, as a means to overcome the problems as described above, such a method as thin depositing metal such as gold (Au) on a surface of an insulating material sample has been employed, but in this case what is observed is not a surface of the sample itself, but that of the gold thin film. Accordingly, observation at a high precision is difficult. As gold acts as an impurity to a wafer in process, the material can not be used after being treated with gold.
However, as the substrate 506 is directly grounded, a large electric field is generated in the gate insulating film 506, which causes such problems as breakage of insulation or deterioration of characteristics of the insulating material.
When taking into consideration that the field of ultra LSIs is becoming increasingly fine and minute, this problem is very serious. The method of using gold deposition to prevent this phenomenon can not be employed because the gold seriously contaminates of the wafers.
This problem caused by electrification occurs in an apparatus in which an electron beam is used, such as a scanning electron microscope (SEM) or an electron beam direct drawing apparatus (EB), or in an apparatus, in which an ion beam is used, such as an ion implanter or a secondary ion mass analyzer.
The present invention was made in the light of the circumstances as described above, and it is an object of the present invention to provide a charged particle flow irradiating apparatus which can prevent electrification of a surface of an insulating material sample.
(Plasma Treatment Apparatus)
In recent years, the degree of integration in LSI has been becoming higher and higher, and active efforts are now made to realize a chip having a size of 1 μm to 0.5 μm or below.
In order to precisely control dimensions of fine chips and to improve the characteristics as well as reliability of the chip as much as possible, it is very important to improve not only the fine manufacturing technology, but also to upgrade various types of materials (such as semiconductor wafers, insulating materials, and metallic thin films) used for production of semiconductor devices.
For this reason, in a process to manufacture ultra LSIs, the importance of using such a thin film forming as etching using electric discharge such as a RIE (reactive Ion Etching) method, a bias sputtering method, or a plasma CVD (Chemical Vapor Deposition) method has increased. A feature of these processes consists in a fact that ions are accelerated by making use of a voltage difference generated between plasma and a wafer and are then irradiated onto a wafer surface. The directivity in etching or qualitative improvement of a grown film is realized by making use of the associated kinetic energy. For this reason, the most important factors in the process as described above include not only a voltage difference between a plasma and a wafer when the plasma is stable but also a voltage in the wafer immediately after the voltage difference between a plasma just generated and a wafer and the plasma has disappeared. A key in the process is to accurately and precisely control these factors.
However, in a currently available process making use of plasma, control over a voltage difference between plasma and a wafer immediately after plasma is generated and control of wafer voltage immediate after the plasma disappeared are extremely inadequate.
Next, a description is made for problems generated when a semiconductor wafer produced by using the conventional technology hereinafter, taking up a case where a silicon thin film is grown by means of the bias sputtering technology.
FIG. 7-3 as a schematic drawing of a bias sputtering device based on a combination of RF and DC. A feature of this device is that argon gas is set in a range from a couple of cc/min to 1000 cc/min and introduced therein through the gas inlet port 302 into the depressurizable vessel 301 to which a vacuum evacuating device having an evacuating speed of 1000 l/sec is connected. In this process, a pressure in the vessel 301 is maintained in a range of several mTorr to 30 mTorr. Plasma is generated by supplying a high-frequency power in a range from several watts to 300 watts and causing argon gas introduced into the vessel 301 to efficiently discharge electricity. To form the Si thin film 309, argon ions (Ar− ions), generated by plasma making use of a voltage difference between a plasma and the target 306, are irradiated onto silicon (Si) target 306 held on the upper electrode 305, and the target 306 is sputtered by making use of the kinetic energy. Si atoms, generated by means of sputtering, run onto a surface of the Si substrate 308 held on the lower electrode and are absorbed in the Si substrate because of the voltage difference generated between the plasma and the silicon substrate.
Resultingly, the silicon thin film 309 is grown. Voltage in the target can be set to an arbitrary value by the DC power source 310, and the target 306 is sputtered efficiently, in practice, by setting the voltage in a range from several V to 1000 V. Also, a voltage in the Si substrate 308 can be set and adjusted by a DC current source 311, a surface of the Si thin film 309 can be sputtered with Ar− ions again by adjusting the voltage in the Si substrate in an appropriate positive value to a negative value, according to the necessity.
However, there are the following problems relating to the conventional technology described above.
As a preprocessing for forming a silicon thin film on a silicon substrate, when a surface of a silicon substrate is cleaned by making use of plasma, it is necessary to maintain a pressure of Ar gas in a depressurizable vessel, for instance, at 5 mTorr and to generate a plasma by setting a high-frequency power with a 100 MHz high-frequency power source. Then a voltage difference between the plasma and the Si substrate is, for instance, 10 V, and a voltage difference between the plasma and the target is, for instance, 40 V.
Under the lower pressure and lower power as conditions for generating plasma, plasma is not generated easily. For this reason, it is necessary to change the initial conditions for generating plasma. If the Ar gas pressure in the depressurizable vessel is raised up to, for instance, 10 mTorr and moreover the high-frequency power is raised up to, for instance, 50 watts, then plasma is easily generated. Then, a voltage difference between the plasma and the Si substrate is, for instance, 30 V, and a voltage difference between the plasma and the target is, for instance, 70 V. When plasma is generated, the initial conditions of Ar gas pressure of 5 mTorr and high-frequency power of 10 watts, which are conditions for cleaning the surface, are immediately restored. As described above, under the initial conditions including a lower pressure and a lower power for generating plasma, plasma is hardly generated.
As such, it is necessary to change the conditions to those under which plasma is easily generated and then return the conditions to the original ones after plasma is generated. In a plasma, if a high-frequency electric field exists between opposing electrodes in a depressurizable vessel into which Ar gas has been introduced, an extremely small number of electrically charged particles existing in the peripheral gas (i.e., Ar gas) are accelerated, execute reciprocal movement between the electrodes, and repeat collision and electrolytic dissociation with neutral atoms or molecules in the gas, so that a number of charged particles rapidly increases, eventually dielectric breakdown occurs, and electric discharge is executed, resulting in a plasma being generated.
When the gas pressure is low, an average free travel of, for instance, electrons in the gas becomes longer, and acceleration in the electric field becomes large. As times of electrons' collisions between the electrodes decrease, so that collision and electrolytic dissociation become are not performed so actively, an electric discharge is hardly generated. For this reason, if a pressure and a power, both of which are conditions for generating plasma, are low, it is required to temporally raise the pressure as well as the power to a high level. When plasma is generated as described above, it is impossible to remove impurities (such as a natural oxide film, oxygen, carbon, and heavy metal) absorbed in or deposited on a surface of a Si substrate. Also, plasma damages are created on the surface of the Si substrate, which in turn results in degradation of a Si thin film's quality. Also, for instance, in case of such a device as a sheet treatment apparatus, a long time is required for processing each sheet, and it is hard to raise the throughput. Further, if a semiconductor device is produced with a Si thin film having a poor quality and a Si substrate with plasma damages therein, a LSI requiring a high speed operation can not work at a required high speed, and also the reliability drops.
Additionally, if plasma processing is executed under a low pressure, space distribution of a plasma becomes more homogeneous, and also an average free travel of ions becomes longer, so reproducibility of homogeneity in film quality becomes higher when producing a thin film. Also, it becomes possible to carry out homogeneous etching with high aspect ratio in isotropic etching by means of the RIE method. However, when a plasma is generated under a low pressure, as the plasma is generated only for a short period of time, if the pressure is raised to a higher level for processing, the plasma space distribution becomes nonhomogeneous. Consequently, a high quality thin film can not be produced, nor can etching be reproduced with high homogeneity. Furthermore, if the Si substrate, itself held on an electrode in a depressurizable vessel, has been electrified before a plasma is generated, once a plasma is generated, a voltage difference between the plasma and the Si substrate is not adjusted to a constant value which is equal to a sum of a DC voltage supplied from the outside and the plasma voltage. As a result, a quality of the Si thin film may become poor.
Also, if a Si film is formed on a Si substrate under certain desirable conditions for plasma generation, when a supply of high-frequency power is stopped and a plasma is caused to disappear after a Si thin film has been formed, a surface of the Si thin film would have been electrified by ions cr electrons in the plasma, and plasma damages would have been generated due to this electrification and the plasma damages would remain in the formed Si thin film.
Additionally, if a surface of the Si thin film has been electrified, particles generated in a vessel while a plasma is generated are deposited on a surface of the Si thin film, etching residue would be generated n a subsequent process such as, for instance, an etching process, and a pattern notch or a pattern bridge would be generated in a photo-lithographic process, and a pattern would not be able to be produced according to the mask.
The present invention was made in the circumstances as described above, and it is an object of the present invention to provide a plasma treatment apparatus which can prevent deposition of particles.
(Electrostatic Absorber)
Conventionally, technologies for separating absorbed materials in an electrostatic absorber are classified to those in which the absorbed materials are forcefully separated by a mechanical means and those in which the residual charge is deleted by an electric means.
Representative ones of the means are as follows.
(1) Mechanism for separation by a mechanical means:
(1-1) Mechanism for forceful separation by a means for giving a mechanical separating force such as a pin which can be thrust out from an absorbing electrode or a piston;
(1-2) Mechanism in which a piezoelectric chip or a ultrasonic vibrator is buried in a surface of an absorbing electrode, with vibration of these chips being used as a means for supplying a separating force; and.
(1-3) Mechanism in which a high pressure gas is filled in a space between an absorbing electrode and a material to be absorbed, with an expanding force generated by the gas pressure being used as a means for creating a separating force; and
(2) Mechanism for separation by an electric means:
(2-1) Mechanism in which an absorbing force is caused to disappear by inverting polarity of voltage loaded to an absorbing electrode and a material absorbed thereto to delete residual charge in an insulating body provided between the two above; and
(2-2) Mechanism in which voltages in an absorbing electrode and a material absorbed to the electrode are adjusted to the ground voltage to delete an absorbing force.
However, as a principle or practical matter there are the following problems in any of the conventional technologies as describe above.
(1) Problems in forceful separation by a mechanical means:
(1-1) A mechanical mechanism using a pin which can thrust out or using a piston therein needs a control section for the pin or piston, so that construction of an electrostatic absorber becomes very complicated Additionally, a mechanically movable section and a sliding section become sources of particles (e.g., minute dust particles), and if the electrostatic absorber is used in a vacuum together with a lubricant, materials absorbed to the electrode such as a silicon wafer can be heavily contaminated. For this reason it has been undesirable to apply this type of electrostatic absorber in a high performance semiconductor manufacturing apparatus.
(1-2) When a piezoelectric chip or a ultrasonic vibrator is buried in an absorbing electrode, an effective absorbing area of the electrode decreases, and it is difficult to finish places where the piezoelectric chip or the ultrasonic vibrator is buried to the same place as an absorbing surface of the electrode and maintain the state. In addition, the capability of absorbing and supporting is impeded when the electrode is heated or cooled, which may sometimes lower reliability of the apparatus.
(1-3) When an absorbed material is separated against an absorbing force of residual charge by an expanding force due to the gas pressure, if the material is a body having a light weight like that of a silicon wafer, the material can be blown up due to transitional expansion of gas immediately when the material is separated, and heavy damages can disadvantageously can be incurred by the material. On the other hand, if the gas pressure is suppressed to a low level to evade the phenomenon as described above, a long time is required until separation is completed, which is an obstacle to be overcome in the practical operation.
Problems in deletion of residual charge by an electric means:
(2-1) When it is tried to delete residual charge in an insulating body by means of inverting polarity of loaded voltage, it is extremely difficult to completely delete the residual charge by executing inversion of the polarity only once. To overcome this problem, a process in which polarity of a loaded voltage is inverted repeatedly to gradually make the value smaller and eventually proceed to zero is indispensable. With this type of polarity inversion method as described above, it is impossible to execute separation instantly, and always a time of a couple of seconds is required.
(2-2) Adjusting voltages in all section relating to electrostatic absorption to the ground voltage is naturally desirable, but in this method a discharge current, which flows for a certain period from the instant of grounding, and also so-called an absorption current are generated. For this reason, 3 to 5 seconds are required before a Coulomb force completely disappears after the voltage in the apparatus reaches the ground voltage.
As there are the problems as described above in both the mechanical means and electric means, a means in which the two technologies above are combined to make up for shortcomings of each technology was once proposed. However, in this case construction of an electrostatic absorber becomes more complicated with the size also becoming larger, which in turn results in higher production cost.
This invention was made in the light of the circumstances described above, and it is an object of the present invention to provide an electrostatic absorber working at a high speed with a simple construction which is applicable to the manufacture of a high performance semiconductor manufacturing apparatus.
(Interatomic Force Microscope)
The following technology is known as an interatomic force microscope.
In this technology, the device for detecting a very minute interatomic force generated between atoms constitutes a probe. Those forces in a surface of a sample, when scanning, are measured with the probe held closer to a surface of the sample (a material to be measured). For instance, a fine surface topography of a metallic sample or an insulating body sample is observed at a high resolution, so that irregularity of a sample's surface can be measured. A principle of an interatomic force microscope is as described below. The reference numeral 401 in FIG. 9-4 denotes a probe having a sharp tip with a full length of several microns, which is made of such a material as silicon nitrate. This probe is formed monolithically with a thin spring 402. The reference numeral 403 denotes a sample which is a material to be measured, which is, for instance, a metallic piece, an insulating body, or a semiconductor. The force working between the probe 401 and the sample 403 changes, as shown by a graph in FIG. 9-5, when a distance between the probe 401 and the sample 403 is changed. In this figure, the X axis shows a distance between the probe 401 and the sample 403 with a point where the force is reduced to zero, as the origin and the direction in which the samples get afar as the positive one. On the other hand, the Y axis shows a force working between the probe 401 and the sample 403. The force, relative to the Y axis, working in the positive direction is a repelling force, while the force working in the negative direction is an attractive force. When the distance between the probe 401 and the sample 403 is reduced to around 100 Å or below, from the utmost surface of the sample, a repelling force works there. The strength of the force is in a range from 10−7 to 10−12 N. This repelling force is converted to a displacement by a weak spring (10 N/m-0.01 N/m) to obtain a force working between the probe 401 and the sample 403. Herein as a method of detecting a displacement of the spring, for instance, an optical lever is used.
FIG. 9-6 is a concept drawing illustrating a case where the entire apparatus has the configuration as described above. In the case shown in FIG. 9-6, a sample can be minutely moved in each of the X, Y and Z directions by using a piezoelectric chip 601 in the XYZ scanning system. This displacement detecting system comprises a laser light source 602 and a laser light detector 603, and these are provided so that a laser light reflected on a upper surface of a spring 605, integrated with a probe 604, will go into a detector. When displacement occurs in a spring due to a force working between the probe 604 and a sample 606, a path of reflected laser light changes according to the displacement of the spring. The displacement of the reflected laser light path is then detected as a change in a quantity of light coming into the detector. As such, the method of obtaining data concerning irregularity of a surface of a sample does not involve directly measuring a displacement of a spring, but instead involves moving a sample 606 in the Z direction according to irregularities of a surface of a sample so that the displacement will always be constant. Namely, a clearance between the probe 604 and a surface of the sample 606 will always be constant, and measuring the piezoelectric control voltage is often used.
However it has turned out that, when an object for measurement comprising an insulating material (especially a non-conductive material) is measured with a conventional type of device, the result of measurement does not always coincide with a practical roughness of a surface of a sample. Namely, it has turned out that the measure value was not accurate. When it is tried to obtain an accurate measured value, sometimes a vast quantity of time may be required, or it may become completely impossible to carry out an accurate measurement. Also, sometimes a control system of the apparatus works to forcefully press the probe to a sample and break the expensive probe.
The present invention and activity has involved strenuous effects to find out the cause, and it has been found that the accurate measurement can not be performed because of the following reasons.
1. When measurement for a conductive samples performed, sometimes the sample may have been electrified, an electrostatic force is generated due to the electrification, and this electrostatic force gives influence to a minute interatomic force, which makes it difficult to detect the interatomic force accurately.
2. Polarization occurs in the conductive sample, and the polarization gives effects to the interatomic force, and as a result measurement thereof becomes inaccurate, and sometimes it becomes impossible to obtain an accurate surface roughness.
So it was tried to remove electric charge from the sample, but removal of electric charge can not always be performed successfully, and even if it is possible, a vast quantity of time is required.
The present invention was made in the light of the circumstances as described above, and it is an object of the present invention to provide an interatomic force microscope which enables an accurate measurement of an interatomic force and/or an accurate measurement of surface roughness, even if a sample to be measured is a non-conductive material.
(X-ray Irradiating Apparatus)
The technology of irradiating X-rays onto a surface of a sample has been used in a wide range for the purpose to execute analysis of a sample or manufacture semiconductor devices. For instance, as a device for irradiating X-rays, an X-ray photo-electronic spectrometer (XPS), Auger electronic spectrometer, X-ray diffraction instrument, and total reflection fluorescent X-ray device (TRXRF) have been known.
The X-ray photo-electric spectrometer or the Auger electronic spectrometer is an analyzer used for elemental analysis of a sample or detailed observation of chemical combination of atoms, while the X-ray diffraction instrument is a device used to measure the structure of a crystal making use of X-ray diffraction generated from the sample. Also, the total reflection fluorescent X-ray device is a device which enables quantitative as well as qualitative measurement of an element by irradiating X-rays onto a surface of a sample and making use of fluorescent X-ray release from the sample.
However, as X-rays are directly irradiated onto a surface of a sample, sometimes the sample is electrified, which gives disadvantageous effects to the X-rays or the photo-electrons. As a result, the XPS can not be used for precise measurement of an insulating material.
Detailed description is made for this problem caused by electrification with reference to FIG. 10-3. FIG. 10-3 is a schematic drawing illustrating a conventional type of XPS. In this figure, the reference numeral 301 is an X-ray gun, and herein the X-ray generated in the X-ray gun above and having a constant level of energy is indicated by the reference numeral 302 and is irradiated onto the sample 303.
When the X-ray 302 is irradiated onto the sample 305, at least one photo-electron 305 is released from the sample's surface 305. This photo-electron 305 is detected by the detector 306, and the result is used to observe a chemical combination of atoms in the sample in detail.
If the sample 303 is a silicon wafer, and the surface is coated with a SiO2 film having a thickness of 1000 μm positive charge 307 is accumulated in the surface of the SiO2 film due to irradiation of X-ray. As the SiO2 film is an insulating one, the charge is never lost due to conduction, and a new electric line of force is generated. Under the influence by this electric line of force (electric field), such effects as change of trajectory of the X-ray 302 or the photo-electron 305 occur. Concretely, if any electric charge remains on a surface of the SiO2 film, the surface potentials of the oxide film changes. With this change, an XPS peak position of the SiO2 layer against the Si substrate shifts, and for instance, a width of an SiO2 spectrum becomes wider due to an electric field generated by the charge.
Conventionally, as a means for solving the problem described above, the technology of irradiating electrons having energy of several eV onto a surface of a sample and neutralizing the sample electrically has been used, but there is no means for making a determination as to whether the surface has completely been neutralized or not. Also, a method of thinly depositing metal such as gold (Au) on a surface of an insulator sample and to make the metallic film electrified like the sample and obtaining a binding energy from a difference between the energy level and that in the inner core has been used. However, the sequence for deposition is troublesome, and also a composition of the sample inevitably changes due to deposition, so that it has been difficult to carry out a precise observation. Also as gold is an impurity to a wafer, this method can not be used for observation of a wafer in a process to manufacture semiconductor devices.
This problem is very serious, because ultra LSIs have been becoming increasingly fine and minute. Use of gold deposition to overcome this problem is impossible, because a wafer is seriously contaminated by gold.
The problem caused by electrification as described above occurs in an apparatus using X-rays therein such as an X-ray photo-electric spectrometer (XPS), an Auger electronic spectrometer, an X-ray diffraction device, and a total reflection fluorescent X-ray device (TRXRF).
The present invention was made in the light of the circumstances as described above, and it is an object of the present invention to provide an X-ray irradiating apparatus which can prevent electrification of a surface of an insulator sample.
(Cleaning Equipment)
Conventionally, the following technology has been used for cleaning a body to be processed (such as a semiconductor). In the technology, chemical liquids such as a mixed solution of sulfuric acid and hydrogen peroxide, a mixed solution of chloric acid and hydrogen peroxide, a mixed solution of ammonia and hydrogen peroxide, a mixed solution of fluoric acid and hydrogen peroxide, and ultra pure water are used in combination to remove organic materials, particles, metals, and natural oxide film deposited on a surface of a semiconductor without removing/affecting the flatness of the semiconductor's surface at an atomic level. The technology includes, for instance, the following steps.
1 (1) Cleaning with a mixed solution of sulfuric acid and hydrogen peroxide (Sulfuric acid:Hydrogen peroxide=4:1, Volumetric ratio) for 5 min., (2) Cleaning with ultra pure water for 5 min;. (3) Cleaning with a mixed solution of sulfuric acid and hydrogen peroxide (Sulfuric acid:Hydrogen peroxide=4:1, Volumetric ratio) for 5 min.; (4) Cleaning with ultra pure water for 5 min.; (5) Cleaning with a mixed solution of fluoric acid and hydrogen peroxide (fluorine acid: 0.5%, Hydrogen peroxide: 10%) for 1 min.; (6) Cleaning with ultra pure water for 5 min.; (7) Cleaning with a mixed solution of sulfuric acid and hydrogen peroxide (Sulfuric acid:Hydrogen peroxide=4:1, Volumetric ratio) for 5 min.; (8) Cleaning with ultra pure water for 10 min.; (9) Cleaning with a mixed solution fluoric acid and hydrogen peroxide (Fluorine acid: 0.5%, Hydrogen peroxide: 10%) for 1 min.; (10) Cleaning with ultra pure water for 10 min.; (11) Cleaning with a mixed solution of ammonia and hydrogen peroxide (Ammonia water:Hydrogen peroxide:Ultra pure water=0.05:1:5, Volumetric ratio) for 10 min.; (12) Cleaning with ultra pure water for 10 min.; (13) Steeping into ultra pure water heated to a high temperature (Approx. 90° C.) for 10 min.; (14) Cleaning with a mixed solution of fluoric acid and hydrogen peroxide (Fluorine acid: 0.5%, Hydrogen peroxide: 10%) for 1 min.; (15) Cleaning with ultra pure water for 10 min.; (16) Cleaning with a mixed solution of chloric acid and hydrogen peroxide (chloric acid:Hydrogen peroxide:Ultra pure water=1:1:6, Volumetric ratio) for 10 min.; (17) Steeping into ultra pure water heated to a high temperature (Approx. 90° C.) for 10 min.; (18) Cleaning with ultra pure water for 10 min.; (19) Cleaning with a mixed solution of fluoric acid and hydrogen peroxide (Fluorine acid: 0.5%, Hydrogen peroxide: 10%) for 1 min.; (20) Cleaning with ultra pure water for 10 min.; and (21) Drying by blowing nitrogen gas thereon for 2 min.
Also, the following first to third technologies have been known as a technology to dry a semiconductor in a cleaning process.
The first technology is a spin drier, in which an object to be cried is momentarily rotated at a high rotating speed to blow off liquid deposited on a surface of the object to be dried with the centrifugal force. In this method, it is possible to dry an object to be dried by blowing off even liquid in very fine concave sections on a surface of the object to be dried, and also it is possible to prevent a natural oxide film from growing on a surface of the object to be dried (such as a silicon wafer) by purging nitrogen gas inside the apparatus. In addition, it is possible to prevent generation of static electricity, as well as to prevent particles from being deposited onto the object to be dried due to static electricity by providing an ionizer having an electrode section coated with a ceramic material and turning an object to be dried at a high rotating speed in the apparatus.
The second technology is an IPA vapor drier, which dries an object to be dried by heating IPA (Isopropyl alcohol) in the apparatus to generate IPA vapor and substituting liquid (for instance, ultra pure water) deposited on a surface of the object to be dried introduced into inside of the apparatus with IPA having a high volatility. As the IPA vapor can go into very minute concave sections in a surface of an object to be dried, it is possible to completely dry even inside of very minute concave sections on the surface of the object to be dried. In addition, IPA has a function to remove static electricity. IPA removes static electricity in a surface of an object to be dried and does not generate static electricity, so that it is possible to eliminate deposition of minute particles onto a surface of an object to be dried due to static electricity.
The third technology is an inert gas drier, which dries an object to be dried by blowing an inert gas (such as a nitrogen gas) to a surface of the object to blow off liquid (such as ultra pure water) deposited on the surface of the object. It is possible to effectively remove molecules remaining on or absorbed in a surface of the object to be dried by reducing a quantity of moisture in the gas to an extremely low level. Also, it is possible to prevent a natural oxide film from growing on a surface of the object by shutting off the apparatus against the external air and providing the inert atmosphere flow.
However, there are the following problems in each of the technologies described above.
At first, in the conventional type of semiconductor cleaning technology as described above, all steps are carried out under illumination, or at least in an environment where no consideration is taken to shut off light from outside, so that a semiconductor, which is an object to be dried or cleaned, is excited by energy of light irradiated thereto. Then, a number of free electrons and holes in the semiconductor increases as compared to those in a semiconductor in an environment where incoming light is shut off. For instance, when a semiconductor having therein a p-type region where boron (B) is added to silicon is placed in an environment where light is irradiated to the semiconductor, electrons excited by the light exchange charge with metallic ions (having a positive charge) in the cleaning liquid, and the metallic ions are absorbed into a surface of the semiconductor. On the other hand, if a semiconductor having an n-type region where phosphor (P) is added to silicon is cleaned in an environment where light is irradiated, holes excited by light exchange electric charge with negative ions (having negative electric charge) in the cleaning liquid, and the negative ions are absorbed onto the surface of the semiconductor.
Furthermore, in the conventional type of semiconductor cleaning technology as described above, at least cleaning with ultra pure water is not carried out in an inert gas atmosphere, so that oxygen in the atmosphere is dissolved into the ultra pure water and a surface of a semiconductor, which is an object to be processed, is oxidized. For this reason a natural oxide film, which degrades characteristics of a semiconductor, grows on the surface of the semiconductor. In addition, when a natural oxide film is growing, a metal such as iron (Fe), aluminum (Al), or sodium (Na), which is oxidized more easily than a semiconductor made of, for instance, silicon, generates a metallic oxide, which is taken into the natural oxide film. As such, a surface of the semiconductor is contaminated. Namely, when a semiconductor is not cleaned in an inert atmosphere, the operation itself promotes growth of a natural oxide film which deteriorates characteristics of the semiconductor and causes metal contamination by taking metallic oxide into the natural oxide film.
In the first drying technology described above, after liquid (for instance, ultra pure water) on a surface of an object to be dried is blown off, some molecules of the liquid may remain on the surface of the object.
In the second drying technology, after liquid (for instance, ultra pure water) on a surface of an object to be dried is substituted by IPA vapor for drying, IPA molecules and molecules of the liquid (for instance, water) may remain on the surface of the object to be dried.
In the third technology as described above, static electricity is generated on a surface of an object to be dried due to frictions between the surface of the object to be dried and gas, so that particles are easily deposited on the surface of the object to be dried.
The present invention was made in the light of the circumstances as described above, and it is an object of the present invention to provide a cleaner which can effectively remove impurities on a surface of a semiconductor, when a semiconductor as an object to be processed, is dried or cleaned. Such drying and/or cleaning needs to be accomplished without causing deposition of impurities on the surface of the semiconductor due to excitation of electrons or holes by light, causing deterioration such as formation of a natural oxide film on the surface of the semiconductor, causing generation of static electricity, nor causing deposition of particles.